In this regard, it was disclosed in DE-OS 255 429 that a force is coupled into the pedal controlling the speed of the vehicle in dependence on the deviation of a parameter of the vehicle (for example, the distance from another vehicle, deviation from a nominal speed). A like function is designated in the following as force-feedback function and mostly referred to as FF function. A pedal equipped with a function of this type is mostly referred to as Force-Feedback-Pedal or FFP.
EP patent 709245 describes how, in the event of exceeding of the nominal speed, a force is exerted computer-controlled on the pedal that controls the speed, said force counteracting the pressure applied by the foot of the driver and thus warning the driver. As the driver has the feeling of having reached already an accelerator pedal position that corresponds to a higher driving speed because a corresponding pedal force is counteracting, the driver is quasi disciplined thereby and induced to observe the speed prescribed or appropriate for safe driving. In this arrangement, a turning lever is coupled to a carburetor cable. When the actual speed is below the nominal speed, a gear will adopt the position as shown in FIG. 1, and the lever is freely movable. The position of FIG. 2 is adopted when the nominal speed is reached, and an adjusting lever will abut on the control lever. When the actual speed deviates further from the nominal speed, a condition as shown in FIG. 3 is adapted, where the adjusting lever is returned counterclockwise by the control lever, with the result that the gas is reduced and the force exerted by the driver becomes ineffective. It is not possible for the driver to increase the speed in excess of the adjusted speed value in case of need.
U.S. Pat. No. 4,367,805 discloses coupling the conduit used to meter the gas with a lever that cooperates with an adjusting lever driven by a motor. The lever is turned to the right upon depression of the pedal. When the cruise control is switched on, the adjusting lever is moved to adopt the position that corresponds to the adjusted speed. The angle of rotation of the adjusting lever depends on the difference between the actual speed and the nominal speed. As long as the actual speed is lower than the nominal speed, the position of the two levers is freely variable. When the nominal speed is exceeded, a spring must be counteracted upon depression of the pedal. As a result, the counterforce rises in dependence on the difference between actual and nominal speeds, an abrupt increase of the restoring force is not intended.
U.S. Pat. No. 5,568,797 discloses adjusting a lever by way of a pedal along with a throttle. Turning the lever to the right means an increase of speed. The nominal speed is adjusted by way of a motor shaft with the indicator secured thereto, and turning to the right implies a higher nominal speed. This prior art device suffers from the following disadvantage: initially, the force of the spring counteracts the restoring force of the spring, then becomes zero, and subsequently acts in dependence on the difference of speeds rising in the direction of the restoring force.
In U.S. Pat. No. 2,822,881, the pre-adjustment is effected by means of a turning plate. An indicator plots the actual speed. When the actual speeds exceeds the nominal speed, the indicator will switch a contact, and a relay will switch on a motor causing a slide to move by means of a rod back against a stop until the actual speed is sufficiently below the nominal speed and the motor is hence switched off.
It has shown that the prior art constructions are rather complicated and costly and do not satisfy a number of demands placed in practical operations (cf. e.g. the demanded course of curve in FIG. 8b). Attention must be paid, among others, that when using an electric motor for providing the FF function, said motor will not be overloaded. Further, care must be taken that the actuator for the FF function or the device is under no circumstances allowed to independently increase the speed of the vehicle, thereby augmenting risks that are to be avoided by the device. In addition, the driver shall keep full control over the vehicle. This means, it must be possible to the driver to apply the accelerator pedal (or brake pedal) to achieve a higher speed or intensified braking even if the FF function has commenced already. This action is referred to as ‘overruling depression’. Furthermore, it must be ensured that the driver notices that the vehicle exceeded the nominal speed. Attention must be paid that the force applied to the pedal at a defined speed can be very different, depending on how much the vehicle is loaded and whether it is driving uphill or downhill.